Upcoming Deadlines Homework #12 – Lighting a Scene in Maya Due Wednesday, December 1 st (Week from...

Upcoming Deadlines

Homework #12 – Lighting a Scene in MayaDue Wednesday, December 1st (Week from today)20 points (10 points if late)

Homework #13 – Creating Stereoscopic 3D ImagesDue Wednesday, December 8th (In two weeks)20 points (10 points if late)

For full schedule, visit course website:ArtPhysics123.pbworks.com

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Homework #12

Light the scene created in your previous homework assignment using one, two, and three-point lighting.

Created by Candace Downey

One-point Lighting:Light the scene with a single bright spot light on the left side; this is your key light.

Homework #12

Created by Candace Downey

Two-point Lighting:Add a dim fill light on the right side to soften the shadows created by the key light.

Three-point Lighting:Add a bright rim light behind the letters to accentuate their edges from the dark background.

Homework #12

Created by Candace Downey

Render the three scenes, save each image, and upload them to your blog.

Due by 8am on Wed., December 1st 20 points (if late, 10)

All Assignments and Extra Credit must be turned in by 5pm on Tuesday, December 14th (day of the final exam)

Final Exam

Final Exam will have of 10 short essay questions on material covered in lecture.Final exam counts for 50 points.

See course website for copy of last semester’s final exam.

You may bring one page of notes double-sided (or two pages single-sided) to the exam.

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Survey QuestionHow much time did this week’s homework (Building a Scene in Maya)

take you to complete?

A) Less than an hourB) Between one and two hoursC) Between 2 and 4 hoursD) Over four hoursE) Didn’t finish that assignment

Finding the Highlight

A B C

D: None of these

LampWhere does Albert see the highlight reflected off this metal block?

Albert

Finding the HighlightLamp

Albert

C Light rays from point C reach Albert.

Review QuestionMatte surfaces, such as paper and cloth, are typically rendered in computer graphics using which shading model?

A)PhongB)BlinnC)ThongD)LambertE)Mambo

Key + Fill

Key only

Review Question

D) Lambert

A Lambert surface scatters light diffusely so under directional light it looks equally bright from all angles.

Johann Heinrich Lambert (1728–1777)

Review Question

What is the shape of the mirrors in these photos?

Concave Mirror

Convex Mirror

A)

B)

OriginalImageMirror

Review Question

A) Concave Mirror

Review Question

The dependence of reflection on angle is called the ______ effect.

Looking straight down into a pool of water we see little reflection of the sky.

Looking at the water at a large angle we see a strong reflection of the sky.

Review Question

Small angleLarge angle

Weak Reflection

Strong Reflection

The dependence of reflection on angle is called the ______ effect.

A) Reflex B) Reflux C) RephaseD) Fresnel E) What-The-Flux

Fresnel Effect

The dependence of reflection on angle is called the Fresnel effect.

Looking straight down into a pool of water we see little reflection of the sky.

Looking at the water at a large angle we see a strong reflection of the sky.

Optics & LightingPart III:

Bending & Scattering

Global Illumination

Notice focusing of light through glass sphere

Without GI With GI

Advanced computer graphics uses global illumination algorithms to compute a more physically realistic rendering of a scene.

Refraction

Light rays bend (refract) passing from water to air, making objects appear to be shallower and closer to the observer.

Image

Actual

Image

Actual

Observer sees image

Reciprocity

Laser

Light bends the same way whether it’s entering the water or coming out of the water.

This symmetry for light rays is called “reciprocity.”

Law of Refraction

Light passing from one material to another is refracted by an angle that depends on the optical density of each material.

Angle is smaller in the denser material.

Demo: Refraction thru a Block

Light is refracted entering the block and refracted back on leaving the block.

Optical Density

Air

Water

Air

Glass

Air

Diamond

n = 1.3

n = 1.0

n = 1.5

n = 1.0

n = 2.4

n = 1.0

Optical density is given by the index of refraction, n.

The larger the difference between the indices at an interface, the larger the angle of refraction for light rays crossing the interface.

Demo: Invisibility

Mineral oil and glass have nearly the same index of refraction

A glass rod is nearly invisible in a beaker of mineral oil.

A diamond, however, is easily seen.

Refraction in a Wedge

Which path does light ray take after entering the glass wedge?

A)Path AB)Path BC)Path C

A

B

C

WEDGE

Path BThe angle always

bends towards the perpendicular going from air to glass.

Notice that it bends away from the perpendicular going back out of the glass.

A

B

C

WEDGE

Refraction in a Wedge

Lenses

Concave lens shrinks its image

Convex lens magnifies its image

Curvature of a lens surface produces a continuous, variable angular refraction.

Demo: Concave Lenses

Curved surface of a concave lens causes light rays to diverge, dispersing the light and shrinking any images.

Demo: Convex Lenses

Curved surface of a convex lens causes light rays to converge, focusing the light and possibly magnifying images.

Camera Lens

Using a lens allows for light to be focused on a screen or camera film.

No image (Diffuse) Camera with lens

Demo: Real Image of Convex LensImage formed by convex lens can be

observed on a screen.

Bokeh Effect (Lens Blur)Point lights expand into balls of light when the light source is out of focus (outside the depth of field).

The term is from the Japanese word boke ( 暈け or ボケ ), which means "blur" or "haze."

Focusing and Shadows

Bright

Dark

When refraction focuses light to create bright areas, it also removes light and creates shadowed areas.

CausticsCaustics are the bright concentrations of light caused by the focusing of that light by refraction or by reflection.

Caustics also create shadow patterns, which visually accent the caustic’s brightness.

Refraction caustics

Reflection caustics

Total Internal Reflection

When refraction angle exceeds 90º the light does not cross the surface.

Refracte

d

ReflectedReflected

Atmospheric Perspective Example

Demo: Total Internal Reflection

Just below critical angle

Past the critical angle all the light is internally reflected.

Demo: Total Internal Reflection

Prism demonstrates total internal reflection if the angle of incidence is large enough.

No light escapes to this side

No light escapes to this side

No light escapes to this side

Looking up Underwater

Try this when you’re in the pool or the ocean next summer.

Looking straight up you see the sky but outside the 96° cone surface is like a mirror

Natural Lighting Underwater

Due to total internal refraction sunlight never enters the water at more than about a 45 degree angle.

Image seen underwater

Sun

Fiber OpticsTotal internal reflection causes light to reflect inside a solid glass tube.

Separating Colors

Blue wavelength of light refracts slightly more than the red, creating rainbows.

Glass Prism

WaterDroplet

RainbowsRainbows are formed by refraction

from many, many raindrops. The red part is always above the blue part.

Double Rainbow

Primary

Secondary

Atmospheric PerspectiveObjects in the distance have a bluish,

unsaturated color due to atmospheric scattering of blue light (same as blue sky).

“Perspective of Color”

Not only did he make good use of what he called “Perspective of Color” but Leonardo also correctly predicted that this is why the sky is blue.

The Virgin of the Rocks, Leonardo, 1482

Light Scattering

Mie ScatteringScattering by particles, such as droplets of fog, of micron size.

Also called Rayleigh-Brillouin Scattering*

Rayleigh Scattering*Refraction by random variations in a transparent medium.

For both types of scattering blue light tends to scatter more strongly than red light.

Mie Scattering

Notice the shadows

Particles in Mie scattering are often transparent or highly reflective.

Suspended Particles

A dust storm is seen from the reflection off the suspended dust particles rather than true scattering.

Mie scattering by water droplets in clouds.

Reflection from suspended particles.

Rayleigh ScatteringSky is blue due to Rayleigh scattering of sunlight in the atmosphere.

When sunlight passes through a very thick layer all the blue is scattered out and we’re left with yellowish red.

Underwater PerspectiveWater is transparent but absorbs red light about x100 more than blue light.

Objects in distance are bluish but saturated.

Significant reflection by suspended particles.

Particles are easily mixed in water due to buoyancy.

Volumetric Lighting

Volumetric lighting is used to create the volume of scattered light, usually due to Mie scattering.

Call of Duty: Black Ops (2010)

http://www.youtube.com/watch?v=l7PRTYn3ZMk

Atmospheric effects are important for creating the right look for this snow level in the game.

Next LectureSeeing Color

Happy Thanksgiving

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